The present invention relates to fluid brake systems. More particularly, the invention pertains to a control valve system including an air biased valve which constantly modulates the pressure of the fluid operating in a brake system which includes a spring applied-pressure released emergency brake mechanism.
Brake control systems for heavy duty earth moving equipment such as trucks sometimes include a pressure reducing valve for controlling the actuation of the service brakes. An example of such a prior art valve may be seen in U.S. Pat. No. 3,259,216 to Klaus et al, of common assignment herewith. Conventionally, the valve spools of such pressure reducing valves have been positioned mechanically by means of a spring disposed between the spool and a mechanical actuating rod or lever connected to an operator brake pedal.
To meet recently enhanced Federal safety regulations, many vehicle manufacturers have provided spring applied-hydraulically released emergency brakes to provide a fail-safe brake system which can be applied to stop a vehicle in the event of failure of the vehicle hydraulic system. It is the control of the application of such spring applied fluid released brake means as well as the control of fluid applied and released brake means to which the instant invention is directed.
Some prior art attempts to provide adequate brake control are taught in U.S. Pat. Nos. 3,650,568; 3,528,707; 3,547,234; and 3,423,136 to Poplawski, Casey, Cummins, and Lohbauer, respectively, all of common assignment herewith.